Since 2012, Espaillat has been gearing up for Round 2. This time, the underdog said he's counting on an upset and making comparisons to one of the biggest ones ever in boxing:

"Sonny Liston was a big, bad bear when he got into the ring, but (Muhammad) Ali was faster, smarter than him," Espaillat said. "He was able to draw circles around him, and he shook up the world and he changed boxing."

If voters want a change now, it may be a measure of how much the district has changed since Rangel went to Washington in 1971.

Harlem's rich African-American history now seems distant

Neal Schumacher knows the streets of Harlem as well as anyone. He gives walking tours, and he often points out the fact that the neighborhood is, "...not the Harlem that I grew up in, but a Harlem I embrace."

A falling crime rate has accelerated real estate development in the neighborhood, but affordable housing remains among the most pressing issues for many with roots in the community.

"People are concerned about gentrification, about rising housing costs, about some of the mom and pop shops closing. About being able to afford to live in the community where you are now," said Schumacher.

Harlem has long been known for its rich African-American history. But to Harlem historian Jacob Morris, that past feels more distant today.

"In the 20th century Harlem was incontrovertibly...the cultural capital of Black America. ...Is it still? I would say now it's the custodian of that great history."

Both say racial and ethnic politics not part of race

Today, the demographics are different. So is the district itself.

Part of the Bronx was added to Harlem's district before the 2012 primary. The 13th Congressional District now has a Hispanic majority.

If elected, Espaillat would become the country's first Dominican-American congressman.

Both candidates insist that racial and ethnic politics shouldn't determine the outcome of the race.

"We never had a political battle in my congressional district in 43 years based on where you were born or what religion you have," Rangel said while campaigning Saturday.

According to a NY1/Siena College poll released the week before the primary, the vast majority of voters said the race or ethnicity of the candidates makes no difference to them,

The same poll shows Rangel has a 70-point lead with blacks and a 5-point lead with whites, while Espaillat has a 24-point lead with Latinos. Overall, the poll gives Rangel a 13-point lead (47%-34%) against Espaillat.

Insiders suggest the race is tighter than that and too tough to predict.

A key factor: turnout is expected to be low. Both campaigns will have to battle to get voters to the polls on Tuesday. The congressional race is the only item on the ballot.